An electric motor is more energy efficient, has more torque, and weighs less than an equivalent fuel burning engine. However, a motor's electrical energy storage supply is often an inferior source of stored energy, making it difficult to effectively replace an engine with a motor.
Electrical energy storage devices are often expensive, large, heavy, and volatile. As a result, over the years these power supplies have become smaller and lighter in order to increase the power to weight ratio. Moreover, there have been several attempts to recover wasted energy, and one of the most prominent sources of wasted energy is braking.
The braking methods for an electric motor usually consist of either frictional, plugging, dynamic, or regenerative braking and each has it's own strengths and weaknesses. Presently, frictional braking is the most reliable. It slows the motor down by converting the motor's kinetic energy into heat, but this kind of mechanism adds weight and requires regular maintenance. Plugging is the use of additional energy to reverse the motor's rotation; which is effective, but also the most wasteful. Dynamic braking and regenerative braking both use the motor's back electromotive force, which reverses the current flow to stop the rotation. Now, even though regenerative braking converts some of the kinetic energy back into electrical energy, the conditions necessary to use this braking method have often hindered its practical use. And while tradition methods of dynamic braking are effective, they do not convert the kinetic energy back into electrical energy.